Quoting from "the success of open source", by Steven Weber, Harvard University Press, 2004, p. 57:
[Software engineer Fred Brooks once] wrote a paper entitled "No silver bullet: essence and accidents of software engineering".One of the goals of The Human Intuition Project is to build a robust framework on which to develop FARG architectures on a much larger and faster scale--or, to use the economist's favorite word, to increase productivity. Brook's distinction is extremely important here. Each project has had its accidental characteristics: NUMBO deals with numbers and operations, Tabletop deals with objects in a dinner table, Phaeaco deals with Bongard problems, Copycat and Metacat deal with letter strings, Letter Spirit deals with font styles, Capyblanca deals with chess, newcoming projects handle music sequences, number sequences, and so forth.
Brooks use Aristotelian language to separate two kinds of problems in software engineering. Essence is the difficulty inherent in the structure of the problem. Accident includes difficulties that in any particular setting go along with the production of software, or mistakes that happen but are not inherent to the nature of the task.
All of these projects have a shared essence; a shared set of ideas employed to create the system. And all of them have accidental characteristics to deal with. If we are successful, then two things will happen: designers of new computational models will be able to concentrate attention to the accidental features of the problem; and, more importantly, we will be able to concentrate on the essential features of human cognition in separation from the accidental features of any particular domain. If we all agree on the same set of ideas, it should be a non-brainer to encapsulate them and have them outside any particular domain and its accidental characteristics.